The present invention generally relates to band compression transmission systems for video signals using sub-Nyquist sampling, and more particularly to a band compression transmission system for video signal using sub-Nyquist sampling in which a video signal is subjected to a sub-Nyquist sampling at a predetermined frequency before being converted into an analog video signal and transmitted, and a receiving side obtains a reproduced video signal by again subjecting the analog video signal to a sub-Nyquist sampling before passing it through a digital-to-analog (D/A) converter.
The sub-Nyquist sampling is conventionally known as a method of sampling a video signal at a sampling frequency which is selected lower than a minimum Nyquist frequency which is a frequency twice a highest frequency f.sub.m necessary for the video signal, and which sampling frequency is also selected to a 1/2 line offset frequency.
The sub-Nyquist sampling utilizes a characteristic which is peculiar to the video signal and is known as frame correlation. The transmission bandwidth can be made very narrow, and it is possible to transmit a broadband video signal in a transmission path which has a narrow bandwidth and to improve the resolution.
However, although the video signal transmission system using the sub-Nyquist sampling has no deterioration due to sampling of still images, the images of each frame differ in the case of dynamic images and the reproduced image becomes a double image with a strong in pression of an afterimage.
In sampling interpolation systems that utilize line correlation, the line correlation can remove the afterimages to a certain extent even in the case of dynamic images but perfect image reproduction is still not possible for images for which there is no line correlation (such as lines inclined at 45.degree.).
Moreover, a luminance/color (Y/C) separation circuit using line correlation cannot perform complete Y/C separation for images that have no line correlation and this results in a carrier chrominance signal being mixed into the luminance signal. This is to say that a beat component is generated for the difference between the chrominance sub-carrier frequency and the sampling frequency used for sampling the luminance signal by the sub-Nyquist sampling. The result of this is the problem known as beat interference that consists of vertical stripes of a relatively wide width appearing on the screen.